Marine Strategy Framework Directive Indicators for Biogenic Reefs formed by Modiolus modiolus, Mytilus edulis and Sabellaria spinulosa: JNCC Report, No. 523

Under the Marine Strategy Framework Directive (MSFD) (Directive 2008/56/EC) Article 10,
Member States are required to establish targets and indicators for the Descriptors of Good
Environmental Status (GES). European and national interpretation of Descriptor 1 on
Biological Diversity provides a strong steer towards indicators of biogenic structures or
‘reefs’. These types of habitat are typically threatened and / or declining, are considered
biodiversity ‘hotspots’, and are often subject to conservation management. In this report we
consider how indicators would best work for habitats formed by the horse mussel (Modiolus
modiolus), the blue mussel (Mytilus edulis) and the ross worm (Sabellaria spinulosa). We
also consider what anthropogenic pressures the indicators would respond to. How these
indicators would be made operational (deployment strategy, timing, resourcing, etc) is the
subject of further work.
Heriot Watt University in association with Pelagica and Salacia Marine reviewed and
analysed the available extant data from survey and monitoring programmes for horse
mussels, blue mussels and ross worm habitats. The available data was drawn largely from
work undertaken by Heriot Watt University, Scottish Natural Heritage, Natural Resources
Wales, Queen’s University Belfast, the Inshore Fisheries and Conservation Authorities and
from studies that were part of the Regional Environmental Characterisation programme. The
present analysis involved accessing thousands of records, scientific samples and images of
biogenic habitats. The project also involved undertaking specific methodological trials on a
horse mussel bed and running a practitioners workshop in Birmingham for 14 experts
involved in blue mussel stock assessment.
Overall, the project considered methods used to assess the density and community
composition of horse mussels, blue mussels and ross worms. The different monitoring and
survey methods were evaluated to test the responses of the ensuing metrics to inherent
temporal and spatial variation as well as the known response to anthropogenic pressures.
Sources of variance were evaluated and the statistical power to detect change was tested.
Recommendations for monitoring methods and metrics for horse mussel, blue mussel and
ross worm dominated habitats are therefore made in this report, as are recommendations for
further research and development. Detailed Procedural Guidelines for recommended
monitoring methods are captured in the Appendices